Q on exporting impulse responses - Home Theater Forum and Systems - HomeTheaterShack.com

 
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post #1 of 4 Old 03-19-12, 08:25 PM Thread Starter
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Gerbrand
 
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Q on exporting impulse responses

Hello,

I am using REW to measure impulse responses and export them for subsequent processing with DRC. I would very much like to take the channel delay into account in DRC. This can be done if the impulse response is measured with respect to an external loopback as a timing reference.

I though I had nailed in when I switched on the "Use Loopback as Timing Reference" in the analysis section. However, this seems to only affect the analysis inside REW. The exported WAV file is not affected: it is always centered on 1 s (sample 96000 in my case).

Is this intended behaviour? Did I miss something here?

Thanks for your help,

Gerbrand
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post #2 of 4 Old 03-20-12, 12:54 AM
SAC
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Re: Q on exporting impulse responses

Are you actually using a loopback for hardware latency?

Merely setting the "Use Loopback as Timing Reference" does nothing if the loopback cable is not physically configured.

And then it only compensates for the hardware propagation latency.

Perhaps John can comment as I am unaware of how DRC processes impulse responses. Or how it deals with the actual time of flight, or...many question predicated on what DRC tries to do.

Last edited by SAC; 03-20-12 at 01:00 AM.
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post #3 of 4 Old 03-20-12, 09:03 AM Thread Starter
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Gerbrand
 
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Re: Q on exporting impulse responses

Hello,

Let me quote from the DRC documentation:
Quote:
First of all the current DRC release is able to compensate for interchannel misalignment of only few samples, no more than 8 with the default configuration files. Furthermore accurate time aligned measurements must be supplied, using either the glsweep and lsconv tools with a reference channel or some other tool providing the same degree of accuracy.
I am trying to achieve the part in bold using REW. I have connected an actual loopback cable from one of the unused channels of my soundcard to the input. When I do this and check "Use Loopback as Timing Reference" REW actually reports my speaker distance correctly. However, this is somehow not reflected in the exported WAV file. The impulse response is still centered on sample 96000. I would expect the impulse response to be centered on sample 96000 + 96000* speaker distance/speed of sound (for 96 kHz sampling).

Actually, this is not a serious issue. I was just wondering if it is intented.

BR

Gerbrand
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post #4 of 4 Old 03-20-12, 04:36 PM
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Re: Q on exporting impulse responses

It is intentional for the exported responses, to ensure the full response is captured - the peak is placed 1 second into the file. If you know the delays (e.g. from the REW figures) the responses could be shifted appropriately in a wav editor, but I suspect DRC offers easier ways to alter relative timing.
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